What confuses me is that it sounds like both Mechs and Constructs will exist. I hope that means Adana won’t be further compromised, or we’ll see a more significant rework of some of their troops. Adana needs the love!

Which is why they aren’t. They’re Fey, which fits them just fine. They’re thematically similar to most other Fey. I don’t see why you would add Mystic to them but not to any other Fey - but that would make Fey redundant.

I think the meaning you are trying to apply to Mystic is already conveyed in the word Fey, and there is no need to add (or replace with) Mystic there. Most likely, Mystic should apply to someone [from a race that is not naturally magical] who practice magic or other mystic arts.